Cool birds: first evidence of energy-saving nocturnal torpor in free-living common swifts Apus apus resting in their nests. (13th April 2022)

• Record Type: Journal Article
• Authors: Wellbrock, Arndt H. J.; Eckhardt, Luca R. H.; Kelsey, Natalie A.; Heldmaier, Gerhard; Rozman, Jan; Witte, Klaudia
• Is Part Of: Biology letters. Volume 18:Number 4(2022)
• Publication Date: 2022-04-13
• Subjects: nest temperature -- metabolic rate -- field study -- CaloBox™ -- hypometabolism -- non-invasive methods; Biology -- Periodicals; 570.5
• DOI: 10.1098/rsbl.2021.0675
• Languages: English
• ISSNs: 1744-9561

Abstract

Abstract : Daily torpor is a means of saving energy by controlled lowering of the metabolic rate (MR) during resting, usually coupled with a decrease in body temperature. We studied nocturnal daily torpor under natural conditions in free-living common swifts Apus apus resting in their nests as a family using two non-invasive approaches. First, we monitored nest temperature ( T nest ) in up to 50 occupied nests per breeding season in 2010–2015. Drops in T nest were the first indication of torpor. Among 16 673 observations, we detected 423 events of substantial drops in T nest of on average 8.6°C. Second, we measured MR of the families inside nest-boxes prepared for calorimetric measurements during cold periods in the breeding seasons of 2017 and 2018. We measured oxygen consumption and carbon dioxide production using a mobile indirect respirometer and calculated the percentage reduction in MR. During six torpor events observed, MR was gradually reduced by on average 56% from the reference value followed by a decrease in T nest of on average 7.6°C. By contrast, MR only decreased by about 33% on nights without torpor. Our field data gave an indication of daily torpor, which is used as a strategy for energy saving in free-living common swifts.